Image processing is often heard of in photography or movies. Scanner plays an indispensable role in this technology. Higher resolution is required to obtain more clear images, but the image files also occupy a larger space in the disk. An A4-size image may be converted into a file of few megabytes when it is scanned with resolution of 600 dpi (dot per inch). Sometimes, an image with lower resolution is allowable so the size of the image file can be reduced very much. The required resolution is various according to circumstances. For example, scanning a usual document requires a lower resolution, but scanning a beautiful photograph needs a higher resolution. Accordingly, the conventional scanner with only one resolution is not proper for all kinds of images. The concept of a scanner with many resolutions has been proposed recently. It is conceivable that some additional elements are needed for "switching" among resolutions to achieve this concept.
A driving element is usually adopted to perform the "switching" function. The word "switching" means that some optical elements will be moved, by the driving element, to be on the optical path according to desired resolution of the scanning operation. It is possible but not commercially practicable because any moving action is unfavorable to the precision of the scanner. Precise locations of the optical elements are very important, but once the optical elements are moved, no one can assure that they would be moved to right positions. A slight error in moving the optical element will cause a serious error in the resulting image file. Apparently, to meet the demand of the public, it is necessary to exercise much effort in manufacturing the conventional scanner with many resolutions, but the scanner is of doubtful utility.
For example, please refer to FIG. 1 which shows how a conventional scanner works. The piece of paper 11 is put on the scanning window and needs to be scanned. If a lower resolution is required, as shown in FIG. 1A, the low-magnifying powered lens 121 of the lens set 12 is moved to be located on the optical path so the charge coupled device 13 receives an image magnified to a smaller size. On the other hand, if a higher resolution is required, as shown in FIG. 1B, the high-magnifying powered lens 122 of the lens set 12 is moved leftwards to be located on the optical path and the charge coupled device 13 receives an image magnified to a larger size. The most serious disadvantage of this method is its unsatisfied precision resulting from moving the lens set 12. The method has further disadvantages. To perform this moving function, additional space is necessary for locating the driving device and for moving the optical elements. It is contrary to the modern machine which is expected to have a minimum size.
There are some Taiwanese Patents showing how to improve such device or method. Taiwanese Patent Publication No. 281851, for instance, provides a method used for scanner, facsimile machine, copy machine, or the like which have optional resolutions. It teaches that both the zoom lens and the charge coupled device are movable wherein they are moved by a driving motor. In order to keep the precision of the machines, a calibrating unit is added. Besides, Taiwanese Patent Publication Nos. 286850 shows that the charge coupled device is moved by a ball screw. Other relevant Taiwanese Patents with Publication No. 232398, 235112, and 280480 teach that lenses are moved by their respective featured driving elements. The advancement of these prior publications would seem as nothing when compared with their large volume, high production cost, and unsatisfied precision.